Insects have been a problem for crops and stored food products since the dawn of agriculture. Since the 1950's synthetic insecticides have been the method of choice to control insect infestations in crop fields, stored grain, warehouses and food processing facilities. However, there are several reasons that alternatives to synthetic insecticides are required. Insects have developed resistance to several synthetic insecticides. Many consumers want no insecticide residues on their food. The application of synthetic insecticides has become more onerous. For example, the fumigant aluminum phosphide in the U.S.A. has a new label which requires more sampling of product and greater notification of the public.
Some insecticides are being phased out because they are harmful to the environment. Methyl bromide, widely used as a fumigant, is an ozone-depleting substance that will be banned after 2005 in most countries. Phosphine, the most widely used grain fumigant, is also being restricted in its use. New protectants are needed that are safe for humans and the environment.
To control insects there are a number alternatives to synthetic insecticides; physical, biological, or botanical. Botanical insecticides have a long history of use in agricultural product protection. Pyrethrums, usually synergized with piperonyl butoxide, are used extensively commercially to control stored-product insects. Neem has been used for centuries in India in stored grain. However, other than spices, food plants have not been widely used to control insects.
It has long been known that legume seeds contain a wide range of chemicals with toxic or deterrent effects against insect pests. For example, pea seeds (Pisum sativum L.) and their extracts are toxic to many insects, especially Sitophilus spp. (Bodnaryk et al, U.S. Pat. No. 5,955,082, issued Sep. 21, 1999; Delobel et al, PCT publication WO99/58695 published Nov. 18, 1999). A multigenic family of small linear, 37-amino acid peptides, was isolated from peas (Higgins et al., 1986) and variants of this cysteine-rich pea albumin (PA1b) were found to be toxic to stored-product insects and aphids (Delobel et al., WO99/58695). Delobel et al. isolated from peas and sequenced an insecticidal variant of PA1b with a mass of 3741 Da. Gressent et al., 2003) have studied the binding of this 3741 variant to microsomal fractions of wheat-feeding and pea feeding weevils. Other legume seeds have been studied genetically for the presence of insect-toxic seed albumins (Louis et al., 2004).
Bodnaryk et al. (U.S. Pat. No. 5,955,082) developed an extraction procedure comprising treatment steps using chloroform and hot 80% methanol to obtain crude insecticidal pea extracts. The aqueous methanol extracts from defatted, protein-rich flour were partially purified with reversed phase C8 silica. Activity was found in fractions obtained by elution of the C8 silica column with methanol. These C8 extracts displayed insecticidal and antifeedant activity against rice weevil [Sitophilus oryzae (L.)] and other stored-product insects but the active ingredients of C8 extracts were not identified. Furthermore, the use and disposal of chloroform is expensive, and insecticides containing residual chloroform may be of limited use, particularly with regard to food-grade crops or products. The use of column chromatography is also expensive and may limit industrial scale-up.
Sitophilus spp., S. granarius (L.), S. oryzae (L.) and S. zeamais Motschulsky, are examples of serious, cosmopolitan pests of stored cereals. Previous work has shown that mixing pea seed with wheat seed at a ratio of 1:1 reduced S. oryzae populations by 70%. However, mixing equal weights of whole peas and wheat is not a practical means for controlling pests.
None of the previous approaches has been adapted for industrial use in controlling insects.
Thus, there is a need for alternative natural extracts and methods of preparing the same, for controlling insect spoilage of agricultural products.